Since 1999 the civilian time and frequency standard in the United States has been NIST-F1, a clock that measures the number of oscillations in a cesium atom's resonant frequency.

Throughout the world, a second is defined as exactly 9,192,631,770 oscillations or cycles of a cesium atom. The more accurately a clock can determine these oscillations, the more accurate the clock.

And the new clock, NIST-F2, is three times more accurate than its predecessor.

"If you could run either of these clocks for 100 million years, NIST-F1 would lose one second, NIST-F2 would lose 1/3 of a second," said Steven Jefferts, lead designer of the NIST-F2.

This substantial, but subtle, improvement in national timekeeping won't affect anyone's life tomorrow, said Jefferts, but it could lead to new technologies down the road.

For example, telecommunications and the electric power grid rely on clocks that can keep time to one-millionth of a second a day, said Tom O'Brian, chief of the NIST time and frequency division. He added that GPS synchronization depends on clocks that keep time to one-billionth of a second a day.

"These technologies keep getting adopted for use in our society, so we have to keep inventing things and making them better," said Jefferts.

Both NIST-F1 and NIST-F2 are what are known as fountain clocks. To accurately measure the length of a second, they start by tossing a ball of 10 million cesium atoms into the air, hitting it with microwaves, and then letting it fall down through a tube where it gets hit by microwaves again. These microwaves change the state of some of the atoms in the ball.

Toward the end of the cesium atom ball's journey, it gets hit by another laser, which allows researchers to see how many of the atoms in the ball are in the new state. This whole cycle happens thousands of times an hour until a microwave frequency is found that changes the most cesium atoms into a new state. That frequency is the natural frequency of the cesium atom, or the frequency used to define a second.

(Confused? The video at the top might help.)

The key advantage NIST-F2 has over NIST-F1 is a vertical flight tube that is chilled to minus- 316 degrees Fahrenheit. In NIST-F1 this tube operates at about room temperature. The cooler tube dramatically reduces background radiation, the researchers said, which in turn reduces the very small measurement errors in NIST-F1.

As exciting as this advance may seem, it is just the tip of the timekeeping iceberg. A revolution in timekeeping is afoot, with labs around the world racing to find ever more accurate ways of measuring the length of a second using different atoms in different frameworks.

"Even as we celebrate the most accurate cesium clock in the world, we have research atomic clocks that are more precise," said O'Brian.

Jefferts suggested even bigger changes may soon be afoot: "Not so far in the future we are going to end up redefining the second," he said.

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